1. Field of the Invention
The invention relates to an optical zoom system for a confocal scanning electron microscope as well as to a confocal scanning electron microscope with such an optical zoom system.
2. Related Art
Confocal scanning electron microscopes, which are normally constructed as laser scanning microscopes, are known in the state of the art, for example, let us cite patent DE 197 02 753 A1 in reference thereto. Most recently, components and technical systems from microscopy, specifically from confocal imaging laser scanning microscopes, have been ever more frequently applied to spectroscopic imaging techniques. In this manner, it is possible to survey the spectroscopic characteristics of a selected specimen region without destroying or touching the probed area. Confocal optic microscopy thereby makes it possible to selectively detect optical signals, which are generated within a confocal volume with limited diffraction whose magnitude lies in the realm of micrometers. Laser scanning microscopes with scanning laser beams and/or with probing feed units can generate high focal resolution for two or three dimensional representations of the specimen under examination. Owing to this characteristic, confocal laser scanning microscopy has nearly asserted itself as the standard for fluorescent probes in the field of biomedical technology.
Normally, laser scanning microscopes are used with interchangeable objectives. Thereby, the problem frequently arises that it is only with great difficulty that constant pupil positions along the optical axis can be achieved within a series of objectives. In some cases, axial differences of 40 mm can occur in the objective chamber, which can be shortened in the conjugate space of the scanning configuration between the scan mirrors by up to 4 mm. Lateral straying of the illuminating beam cone from the pupil associated with such a mismatch of the pupil's position can lead to non-uniform illumination of the specimen during scanning.